Piezoelectric materials have been utilized widely in sensors and actuators. Compared to commonly used piezoelectric structures, such as those based on bulk and thin films, piezoelectric fibers have attracted more attention because they allow greater flexibility in the design and application of various structures. Such fibers can be made of a number of materials, such as zinc oxide (ZnO), barium titanate (BaTiO3), lead zirconate titanate (PbZr1-xTixO3, PZT) or a piezoelectric polymer such as polyvinylidine fluoride (PVDF). In particular, fibers made of PZT have provided the basis for devices having high bandwidth, fast response, and high sensitivity.
While there are many methods for fabricating piezoelectric fibers having microscale dimensions, there are few methods for fabricating piezoelectric nanofibers (i.e., fibers having dimensions on the order of nanometers), including hydrothermal synthesis, sol electrophoresis and metallo-organic decomposition (MOD) electrospinning. Fibers fabricated by the hydrothermal and electrophoretic methods are discontinuous, which limits their usefulness as components of working devices. In contrast, the electrospinning method can fabricate continuous fibers having diameters from tens to hundreds of nanometers. Further, aligned fibers can be fabricated using simple auxiliary methods.
Piezoelectric fibers, in general, have been used in active fiber composites (AFC) as sensors and actuators. AFC typically comprise piezoelectric fibers in a polymer matrix, and are more flexible and robust than monolithic piezoelectric devices because they combine the physical properties of the fibers and the matrix. Devices known in the prior art have used fibers with diameters as small as 30 microns, but such fibers are too large to be embedded in active structures or micro or nanoscale devices. Further, AFC typically incorporate interdigitated electrodes to simplify fabrication and take advantage of the non-isotropic character of the piezoelectric properties of the fiber.